The present invention relates to interconnecting devices, and more particularly to programmable integrated-circuit switches.
Many electrical systems such as computer systems are made in different versions which differ from each other by the amount of available memory, the number and availability of peripheral devices, the address space occupied by a particular memory, for example, by a graphics controller memory, or other features.
In order to simplify the manufacturing and reduce the manufacturing costs, different versions are assembled on identical printed circuit boards and each version is configured by mechanical DIP switches (or "jumpers") that establish electrical connections appropriate for that version. A DIP switch is a piece of wire soldered into the printed circuit board to provide an electrical connection. While using identical circuit boards makes the manufacturing simpler and cheaper, the mechanical procedure of soldering the DIP switches places a limit on the speed, reliability and cost effectiveness of the manufacturing process.
In some systems, the DIP switches have been replaced by integrated circuit devices including a read-only memory (ROM) or a programmable read-only memory (PROM). A ROM is mask programmed during manufacturing, and a PROM is programmed after manufacturing by a device ("programmer") which generates a super high programming voltage to blow selected memory fuses. The memory (ROM or PROM) drives a logic which establishes electrical connections in accordance with the memory contents. The memory is programmed as appropriate for the particular version.
A disadvantage of the ROM and PROM based switches is that their versatility in establishing connections is proportional to the complexity of the memory-driven logic that establishes the connections. Moreover, the need for a programmer or for a mask-programming process to program the memory complicates the system manufacture and increases the manufacturing cost.
Thus, there is a need for a simple, versatile integrated circuit switch that can be programmed without a programmer and without a special manufacturing process such as a mask-programming process.